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authorKees Cook <keescook@chromium.org>2022-10-27 01:31:11 +0200
committerKees Cook <keescook@chromium.org>2022-11-01 18:04:52 +0100
commit5a17f040fa332e71a45ca9ff02d6979d9176a423 (patch)
tree976a0250731074e8689c74665873f3b77f0b60c6 /fs/nfsd/nfs4callback.c
parentfortify: Do not cast to "unsigned char" (diff)
downloadlinux-5a17f040fa332e71a45ca9ff02d6979d9176a423.tar.xz
linux-5a17f040fa332e71a45ca9ff02d6979d9176a423.zip
cred: Do not default to init_cred in prepare_kernel_cred()
A common exploit pattern for ROP attacks is to abuse prepare_kernel_cred() in order to construct escalated privileges[1]. Instead of providing a short-hand argument (NULL) to the "daemon" argument to indicate using init_cred as the base cred, require that "daemon" is always set to an actual task. Replace all existing callers that were passing NULL with &init_task. Future attacks will need to have sufficiently powerful read/write primitives to have found an appropriately privileged task and written it to the ROP stack as an argument to succeed, which is similarly difficult to the prior effort needed to escalate privileges before struct cred existed: locate the current cred and overwrite the uid member. This has the added benefit of meaning that prepare_kernel_cred() can no longer exceed the privileges of the init task, which may have changed from the original init_cred (e.g. dropping capabilities from the bounding set). [1] https://google.com/search?q=commit_creds(prepare_kernel_cred(0)) Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: David Howells <dhowells@redhat.com> Cc: "Rafael J. Wysocki" <rafael@kernel.org> Cc: Steve French <sfrench@samba.org> Cc: Ronnie Sahlberg <lsahlber@redhat.com> Cc: Shyam Prasad N <sprasad@microsoft.com> Cc: Tom Talpey <tom@talpey.com> Cc: Namjae Jeon <linkinjeon@kernel.org> Cc: Trond Myklebust <trond.myklebust@hammerspace.com> Cc: Anna Schumaker <anna@kernel.org> Cc: Chuck Lever <chuck.lever@oracle.com> Cc: Jeff Layton <jlayton@kernel.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: Eric Dumazet <edumazet@google.com> Cc: Jakub Kicinski <kuba@kernel.org> Cc: Paolo Abeni <pabeni@redhat.com> Cc: "Michal Koutný" <mkoutny@suse.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: linux-cifs@vger.kernel.org Cc: samba-technical@lists.samba.org Cc: linux-nfs@vger.kernel.org Cc: netdev@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org> Acked-by: Luis Chamberlain <mcgrof@kernel.org> Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org> Acked-by: Russ Weight <russell.h.weight@intel.com> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Acked-by: Paulo Alcantara (SUSE) <pc@cjr.nz> Link: https://lore.kernel.org/r/20221026232943.never.775-kees@kernel.org
Diffstat (limited to 'fs/nfsd/nfs4callback.c')
-rw-r--r--fs/nfsd/nfs4callback.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
index f0e69edf5f0f..4a9e8d17e56a 100644
--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -870,7 +870,7 @@ static const struct cred *get_backchannel_cred(struct nfs4_client *clp, struct r
} else {
struct cred *kcred;
- kcred = prepare_kernel_cred(NULL);
+ kcred = prepare_kernel_cred(&init_task);
if (!kcred)
return NULL;